For rack power in telephone exchanges, it is known to utilize DC/DC converters, which convert an available supply voltage (e.g., -48 V) to a smaller and stabilized valve (e.g., +5 V). The flyback DC/DC converter of the type mentioned is suitable because of its small space requirements and small number of components. As distinguished from other kinds of converters, a flyback converter has a smaller number of power semiconductors and magnetic components and is simpler to operate. It is furthermore easy to provide with several outputs.
According to a principle for such a converter, the power transistor therein is driven to alternating between conducting and non-conducting states. When the transistor is conducting, energy is stored in a magnetic component (e.g., a transformer or inductance) and the load is disconnected. When the transistor is non-conducting, the magnetic energy of the magnetic component is supplied to the load. In the literature, the flyback converter is also known as a DC/DC converter with rectification during return or flyback.
There is an output filter for filtering the output voltage, and an input filter for preventing transients from the switching circuits from reaching the supply voltage source. Both these filters usually utilize capacitors, and a troublesome ripple current can occur, especially in the capacitors of the output filter.